Traditionally, many airline carriers manually assign routes to aircraft. This usually involves having experts allocate all candidate flight segments to specific aircraft tail numbers (unique sequence of alphanumeric characteristics used to identify a specific aircraft) within a given sub-fleet of the airline. In addition to any requirements of the flight segments, the experts must ensure the allocations meet the operational and maintenance requirements of the aircraft. Considering that some carriers may have hundreds of aircraft and thousands of flights scheduled over a given time period (e.g., a month), this can be a complex and cumbersome process. This problem is not necessarily unique to the airline industry, it applies to carriers of other modes of transportation.
Further, during the normal operations of a carrier, situations may often develop wherein modifications have to be made to the existing schedule plan. For example, an aircraft may unexpectedly be grounded, thus leaving all flights that were assigned to the aircraft's route without an aircraft. Since most carriers would not willingly give up the revenues generated by the flights, experts must re-allocate and shift resources in order to accommodate the orphaned flights. If this happens only on rare occasions, then the traditional manual approach might be acceptable.
In other instances, however, airlines may find it necessary to adjust their flight schedules on a regular basis. For example, passenger demand may require daily adjustments to flight schedules because the demand inherently varies over the course of the week. Manually re-planning the assignments of the aircraft and flights to accommodate these adjustments may be inefficient. Further, given the necessity to produce a plan within short time constraints, a generated plan may not be fully calculated to maximize revenues for the airline.
Civil aviation regulations require that all aircraft undergo maintenance after a certain number of flying hours, cycles, and calendar dates. If certain checks are not performed within the specified period, civil aviation authority rules prohibit the aircraft from flying. Thus an airline often schedules aircraft maintenance earlier than required to provide some slack (e.g., extra flying hours) if a routing is disrupted and more flying is needed to arrive at the maintenance station. Airlines typically route aircraft to satisfy a prescribed pattern of movement throughout their network system to ensure that it is possible to conduct maintenance events. Maintenance events beyond nominal line maintenance are usually pre-assigned by the maintenance and engineering department, and it is the responsibility of the maintenance tracker in the airline operations control center to make sure maintenance requirements are met. Accordingly, the aircraft tail assignment process does not usually allow the tracker to modify the existing plan for other than nominal maintenance events.